1. Field of the Invention
The present invention relates to a camera capable of recording information about the position of a principal object to be photographed present in a photographic image plane and, more particularly, to a camera capable of recording information about the position of a principal object to be photographed, which is required to perform proper exposure in printing after photography, and a method of recording the information.
2. Description of the Related Art
Recently, cameras which use a silver salt film in photography and record photographic information on the film have been developed. A film used in a camera of this type includes an information recording portion, such as a magnetic recording portion, for writing various information. A camera system which records position information of a principal object to be photographed present in a photographic image plane, as one information to be recorded, is also known.
For example, Jpn. Pat. Appln. KOKAI Publication No. 3-51839 discloses a camera which records information indicating whether a principal object to be photographed exists in the center of a photographic image plane. Also, Jpn. Pat. Appln. KOKAI Publication No. 3-131840 discloses a system in which position information and luminance information of a principal object to the photographed in a photographic image plane are recorded by using an AF (Automatic Focusing) technique based on multi-distance measurement during photography, and in printing after the photography, these pieces of information are read out to determine a printing exposure amount for mainly the principal object, thereby printing the picture.
In photographing a principal object to be photographed not present in the center of a photographic image plane, the general approach is as follows except in some gaze-sensing, automatic focusing cameras. That is, a user locks the focus with a principal object to be photographed present in a central focusing area (in which distance measurement for automatic focusing is performed) of a photographic image plane and then takes a picture after changing a field angle meeting the intended composition. In executing a photographing method of this type, it is useful to detect position information of a principal object after the field angle is changed and record this information, together with luminance information, in an information recording portion of a film, in order to apply the method to a system using the printing method described above.
Unfortunately, the position information obtained in conventional techniques is in many cases information simply indicating whether a principal object to be photographed is present in the center of a photographic image plane during focus lock. Also, AF by three-point distance measurement is the main stream in compact cameras using the multi-distance measurement AF. Consequently, the position information obtained by this technique is very coarse, and the information can be obtained only by an AF camera which performs the multi-distance measurement.
That is, in conventional techniques, no method is established which detects position information of a principal object to be photographed after a field angle is changed, i.e., the moving amount of the principal object in a photographic image plane. Therefore, no conventional techniques can be usefully applied to the system mentioned above.